1. Field of the Invention
The present invention relates to a cutting tool of polycrystalline diamond having excellent edge sharpness, which is optimum for finishing a work piece of a nonferrous metal or a nonmetal, and a method of manufacturing the same.
2. Background Information
Diamond, which has high hardness as well as high heat conductivity, is applied to a cutting tool or a wear resisting tool. However, monocrystal diamond is disadvantageously cloven. In order to suppress such a disadvantage, there has been developed a diamond sintered body which is obtained by sintering diamond by a very high pressure sintering technique, as described in Japanese Patent Publication No. 52-12126 (1977).
As to commercially available diamond sintered bodies, it is known that particularly a fine-grained sintered body having a grain size of not more than several 10 .mu.m is not subject to cleavage as observed in the aforementioned monocrystal diamond, and exhibits excellent wear resistance.
However, since such a diamond sintered body contains several percent to several 10 percent of a binder, chipping is inevitably caused in units of the grains forming the same. Such a chipping phenomenon is remarkably increased as a wedge angle of the tool cutting edge is reduced, and hence it is extremely difficult to manufacture a tool having a sharp cutting edge. Although it is possible to grind the cutting edge with a fine-grain diamond grindstone of #3000 to #5000, for example, in order to suppress chipping of the cutting edge in a manufacturing process of the cutting tool, such chipping of the cutting edge cannot be suppressed to below 5 .mu.m even if this method is employed. In the method of grinding the cutting edge with a fine-grain diamond grindstone, a new problem is caused in that the working efficiency is reduced as the grain size of the grindstone becomes smaller.
In a known method of working a diamond sintered body, electrical discharge machining or laser beam machining is employed in place of the aforementioned grinding. In the existing circumstances, however, it is impossible to obtain a tool having excellent edge sharpness by such machining, since the diamond sintered body contains a binder.
The inventors have devised a cutting tool, which is prepared from a tool material of polycrystalline diamond containing no binder, i.e., polycrystalline diamond synthesized by a low-pressure vapor phase method, in place of a diamond sintered body. Japanese Patent Laying-Open Gazette No. 1-212767 (1989) discloses an exemplary cutting tool which is prepared from a material of such polycrystalline diamond.
However, in such a cutting tool of polycrystalline diamond, the cutting edge is chipped by about 5 .mu.m when the same is formed by grinding, and it is impossible to suppress such chipping.